12-UN Thread (USA)

The 12-UN thread is part of the series of American UN threads with constant pitch. These are thread standards that each combine various outer diameters with the same pitch. In addition to the thread count of 12 per inch, as in the 12-UN thread, this series also includes threads with 4, 6, 8, 16, 20, 28, and 32 threads per inch. In this context, you might also read the English term 'threads per inch' (TPI), which simply means threads per inch. The dimensions of the 12-UN thread are set according to the ANSI/ASME B1.1 standard by the American Society of Mechanical Engineers (ASME) and monitored by the American National Standards Institute (ANSI).

The 12-UN thread has a flank angle of 60°. It is an imperial thread. The abbreviation 12-UN refers to the constant value of 12 threads per inch for this UN thread and is also stated in the thread designation. The outer diameter is stated first, so a designation would be, for example, 3/4″ – 12-UN.

For some combinations of outer diameter and 12 threads per inch, it may happen that they are already covered by other American thread standards such as UNC, UNF, or UNEF threads. Then these threads are assigned to the mentioned standards and not to the 12-UN thread. Furthermore, the range of outer diameters only includes those values that are structurally sensible in connection with 12 threads per inch. This results in a range of the 12-UN thread table from 5/8″ to 6″.

In the thread table below for the 12-UN thread, you will find the dimensions for the outer diameter in inches and converted to mm. We have also translated the constant pitch of 12 threads per inch into a metric value. Also listed is the core hole diameter. If you need dies or taps for the 12-UN thread, a click on one of the links in the table will take you to the right shop page.